The invention resides in an apparatus for the electrographic printing or copying of images wherein a toner is applied to a medium corresponding to an object to be printed or copied and is fixed on the medium by heat supplied by a hot air blower directing the hot air onto the medium.
Such an apparatus is known for example from DE 26 13 066 A1. In the known apparatus, the air heated by a heating device of the blower is conducted along the medium provided with the toner. The heating device and the blower are arranged in a closed-circuit channel which includes a straight section through which the medium provided with the toner is moved.
Since, with the closed channel, a closed circuit is provided, the thermal losses of the known apparatus are small but the closed circuit results in a contamination of the interior of the closed channel as well as the elements disposed therein which are contaminated by toner released from the medium provided with the toner. In order to prevent the occurrence of malfunctions as a result of this contamination, the elements disposed in the channel have to be cleaned regularly. In addition the contamination of the elements disposed in the channel detrimentally affects their service life.
DE 100 43 033 A1 discloses another apparatus wherein the toner is fixed on the medium to be imprinted by a flashlight. This provides for good results but has the disadvantage that, with a color print, the heat input to the differently colored image areas is different since the heat absorption capacity of different colors, in particular light colors, of the imprinted image is differs from that of other colors, in particular dark colors.
This problem does not occur in connection with printing or copying apparatus wherein heat is applied to the medium, to be imprinted by means of heated rollers. But the use of heated roller for the fixing of the image is suitable only for paper as the medium to be imprinted. However, on metal parts for example, images cannot be fixed by heated rollers.
It is further known to fix the toner on the medium to be imprinted by infrared radiation. Fixing by infrared radiation however has the disadvantage that it is slow which is particularly problematic if the printing speed changes. Furthermore, fixing by infrared radiation is not suitable for high printing speeds.
JP 2000 267 477 A further discloses an apparatus for the electrographic printing or copying wherein toner can be applied to a medium in accordance with an object to be printed or copied and can be fixed on the medium by heat. The apparatus includes a hot air blower by which heated air is directed onto the medium to which the toner has been applied. The hot air blower takes in air from the ambient.
A similar apparatus is also known from JP 57 124 770.
Furthermore, U.S. Pat. No. 4,537,492 A discloses a heat fixing station wherein copying paper is moved over heated plates for fixing. The apparatus includes among others a blower by which the copying paper is pressed onto the heated plates.
It is the object of the present invention to provide an apparatus of the type mentioned above in such a way that a color independent fixing is achieved.